Liquid-crystal display devices have been widely used to display images on mobile phones, tablet terminals, personal computers, car navigations, and other such devices. Such liquid-crystal display devices employ a planar light unit disposed on the back side of a liquid-crystal display panel to emit light in a planar fashion.
In some cases, in order to make the planar light units thinner, a light source is disposed on a side edge (hereinafter referred to as “light incident portion”) of a light guide plate, and light is allowed to enter a light incident surface of the light incident portion and to exit through a main surface (hereinafter referred to as “light exit surface”) (the method by which the light that has entered through the side edge of the light guide plate exits through the light exit surface of the light guide plate will be hereinafter referred to as “sidelight method”). The planar light units employing this sidelight method are faced with a problem in improving luminous efficiency and brightness uniformity on the light exit surface, and various proposals have been made on this problem (for example, patent document 1).
A planar light unit recited in patent document 1 will be described below by referring to the drawings.
FIG. 21 is a perspective view of a light guide plate 120, which is included in the planar light unit recited in patent document 1. The light guide plate 120 is made by processing a light-transmitting resin such as an acrylic resin into a planar shape. A light incident portion 121 of the light guide plate 120 includes a recess 122, to which an LED 111 is to be inserted. On the top and bottom of the recess 122, reflecting-shaped portions 123 are formed. A sectional view of the light guide plate 120 along its light propagation direction shows that the reflecting-shaped portions 123 are curved portions at the top and bottom of the light guide plate 120.
FIG. 22 is a partial sectional view of a surrounding area of the light incident portion 121 of the light guide plate 120 illustrated in FIG. 21, with the LED 111 mounted in the recess 122. The portion illustrated in FIG. 22 will be hereinafter referred to as “light source 130”. The light source 130 includes the recess 122, the light incident portion 121, a light source board 110, the LED 111 (semiconductor light-emitting device), and a microlens 131. The reflecting-shaped portions 123 include the light incident portion 121. The LED 111 is mounted on the light source board 110. The microlens 131 covers the LED 111.
A plurality of LEDs 111, not illustrated, are arranged in a row on the light source board 110, which has a rectangular plate shape. The LEDs 111 include a red LED, a green LED, and a blue LED, which emit different colors. The light source board 110 is attached to the light incident portion 121 with double-sided tape. The recess 122 houses each of the LEDs 111.
In the above-described planar light unit, since the LEDs 111 are housed in the recess 122, light emitted from the LEDs 111 enters the light guide plate 120 efficiently. Moreover, the reflecting-shaped portions 123 totally reflect the light that would otherwise leak from the light guide plate 120 and confine the light to the light guide plate 120. In this manner, the planar light unit improves the use efficiency.